Method and apparatus for optimizing vagal nerve stimulation using laryngeal activity

ABSTRACT

A neural stimulation system delivers neural stimulation to the vagus nerve and senses a signal indicative of laryngeal activity resulting from the neural stimulation. The signal indicative of laryngeal activity is used, for example, to guide electrode placement, determine stimulation threshold, detect lead/electrode problems, detect neural injury, and monitor healing processing following the electrode placement inside the body of a patient.

TECHNICAL FIELD

This document relates generally to neural stimulation and particularlyto a system and method for optimizing vagal nerve stimulation using anactivity sensor that senses a signal indicative of laryngeal activity.

BACKGROUND

Vagal nerve stimulation has been applied to modulate various physiologicfunctions and treat various diseases. One example is the modulation ofcardiac functions in a patient suffering heart failure or myocardialinfarction. The myocardium is innervated with sympathetic andparasympathetic nerves including the cardiac branches of the vagusnerve. Activities in the vagus nerve, including artificially appliedelectrical stimuli, modulate the heart rate and contractility (strengthof the myocardial contractions). Electrical stimulation applied to thevagus nerve is known to decrease the heart rate and the contractility,lengthening the systolic phase of a cardiac cycle, and shortening thediastolic phase of the cardiac cycle. This ability of the vagal nervestimulation is utilized, for example, to control myocardial remodeling.

In addition to treating cardiac disorders such as myocardial remodeling,vagal nerve stimulation is also know to be effective in treatingdisorders including, but not limited to, depression, anorexianervosa/eating disorders, pancreatic function, epilepsy, hypertension,inflammatory disease, and diabetes. The intended therapy outcomes ofvagal nerve stimulation in treating such disorders may be difficult tomeasure, either acutely or chronically, for purposes of therapytitration or optimization. Therefore, there is a need for titrating oroptimizing vagal nerve stimulation using parameters other than theintended therapy outcomes.

SUMMARY

A neural stimulation system delivers neural stimulation to the vagusnerve and senses a signal indicative of laryngeal activity resultingfrom the neural stimulation. The signal indicative of laryngeal activityis used, for example, to guide electrode placement, determinestimulation threshold, detect lead/electrode problems, detect neuralinjury, and monitor healing processing following the electrode placementinside the body of a patient.

In one embodiment, a neural stimulation system includes an activitysensor and a neural stimulation analyzer. The activity sensor senses asignal indicative of laryngeal activity. The neural stimulation analyzerincludes a laryngeal activity input to receive the signal indicative oflaryngeal activity, a neural stimulation input to receive a signalindicative of the delivery of the neural stimulation to the vagus nerve,and a processing circuit. The processing circuit processes the signalindicative of laryngeal activity for analyzing the neural stimulationsystem using the signal indicative of laryngeal activity.

In one embodiment, a neural stimulation system includes an activitysensor, a signal conditioning circuit, a neural stimulation circuit, anda presentation device. The activity sensor senses a signal indicative oflaryngeal activity. The signal conditioning circuit conditions thesignal indicative of laryngeal activity. The neural stimulation circuitdelivers neural stimulation to the vagus nerve. The presentation devicepresents indicators of the laryngeal activity and the delivery of theneural stimulation.

In one embodiment, a method for applying neural stimulation is provided.A signal indicative of laryngeal activity is sensed. The neuralstimulation is delivered to the vagus nerve. The signal indicative oflaryngeal activity is conditioned to isolate laryngeal activityresulting from the delivery of the neural stimulation.

This Summary is an overview of some of the teachings of the presentapplication and not intended to be an exclusive or exhaustive treatmentof the present subject matter. Further details about the present subjectmatter are found in the detailed description and appended claims. Otheraspects of the invention will be apparent to persons skilled in the artupon reading and understanding the following detailed description andviewing the drawings that form a part thereof. The scope of the presentinvention is defined by the appended claims and their legal equivalents.

BRIEF DESCRIPTION OF THE DRAWINGS

The drawings illustrate generally, by way of example, variousembodiments discussed in the present document. The drawings are forillustrative purposes only and may not be to scale.

FIG. 1 is an illustration of an embodiment of a neural stimulationsystem and portions of an environment in which the neural stimulationsystem is used.

FIG. 2 is an illustration of another embodiment of the neuralstimulation system and portions of the environment in which the neuralstimulation system is used.

FIG. 3 is a block diagram illustrating an embodiment of portions of acircuit of the neural stimulation system of FIG. 1.

FIG. 4 is a block diagram illustrating an embodiment of portions of acircuit of the neural stimulation system of FIG. 2.

FIG. 5 is an illustration of an embodiment of a laryngeal activitysensor assembly of the neural stimulation system.

FIG. 6 is an illustration of another embodiment of the laryngealactivity sensor assembly of the neural stimulation system.

FIG. 7 is an illustration of an embodiment of an activity sensorincluding a sensor base.

FIG. 8 is an illustration of another embodiment of the activity sensorincluding the sensor base.

FIG. 9 is a block diagram illustrating an embodiment of a processingcircuit of a neural stimulation analyzer of the neural stimulationsystem.

FIG. 10 is a block diagram illustrating an embodiment of a userinterface of the neural stimulation system.

FIG. 11 is an illustration of an embodiment of an external programmer ofthe neural stimulation system.

FIG. 12 is a flow chart illustrating an embodiment of a method foranalyzing effect of vagal nerve stimulation using a signal indicative oflaryngeal activity.

FIG. 13 is a flow chart illustrating an embodiment of a method forautomatically determining a stimulation threshold for the vagal nervestimulation using the signal indicative of laryngeal activity.

FIG. 14 is a flow chart illustrating an embodiment of a method formonitoring and titrating the vagal nerve stimulation acutely andchronically using the signal indicative of laryngeal activity.

DETAILED DESCRIPTION

In the following detailed description, reference is made to theaccompanying drawings which form a part hereof, and in which is shown byway of illustration specific embodiments in which the invention may bepracticed. These embodiments are described in sufficient detail toenable those skilled in the art to practice the invention, and it is tobe understood that the embodiments may be combined, or that otherembodiments may be utilized and that structural, logical and electricalchanges may be made without departing from the spirit and scope of thepresent invention. References to “an”, “one”, or “various” embodimentsin this disclosure are not necessarily to the same embodiment, and suchreferences contemplate more than one embodiment. The following detaileddescription provides examples, and the scope of the present invention isdefined by the appended claims and their legal equivalents.

This document discusses a system providing for optimization of vagalnerve stimulation using a laryngeal activity sensor. The optimizationincludes, for example, optimization of electrode placement, automaticthreshold determination or verification, monitoring of lead/electrodestatus, detecting of neural injury, and monitoring a healing processthat follows the electrode placement. In many applications of vagalnerve stimulation, the target response (intended outcome) may bedifficult to monitor and analyze for the purpose of therapyoptimization. For example, a transvenous lead is used to deliver vagalnerve stimulation for controlling cardiac remodeling. The transvenouslead includes one or more electrodes at its distal end to be placedwithin an internal jugular vein adjacent to the vagus nerve in thecervical region. The internal jugular vein is a large vessel providingfor a wide range of possible electrode positions. It is practicallydifficult to use effects of the vagal nerve stimulation in cardiacremodeling for guidance in the electrode placement and stimulationparameter adjustment.

On the other hand, it is known that vagal nerve stimulation causesvibration of the larynx through the recurrent laryngeal nerves, whichare branches of the vagus nerve that innervate the larynx. Thus,laryngeal activity, including the magnitude and frequency of thevibration of the larynx, provides for an indication of whether the vagusnerve is activated by neural stimulation. This allows for optimizationof therapy without the need to monitor and analyze the target response(such as cardiac remodeling) of the vagal nerve stimulation.

The present subject matter is applicable to stimulation of the vagusnerve using various energy forms and various signal morphology. In oneembodiment, vagal nerve stimulation includes delivery of electricalpulses to the vagus nerve to artificially elicit action potentials inthat nerve. In other embodiments, vagal nerve stimulation includesdelivery of any form of energy that is capable of eliciting ormodulating neural activities in the nervous system, such as mechanical,thermal, optical, chemical, and biological energies.

The present subject matter is applicable to neural stimulation systemsproviding for activation and/or inhibition of the vagus nerve fortreatment of various disorders including, but not limited to, cardiacremodeling, depression, anorexia nervosa/eating disorders, pancreaticfunction, epilepsy, hypertension, inflammatory disease, and diabetes. Ingeneral, the present subject matter is applicable to any systemproviding for vagal nerve stimulation in which the neural stimulationresults in detectable laryngeal activity.

While delivery of neural stimulation through a transvenous lead havingone or more electrodes placed in an internal jugular vein adjacent tothe vagus nerve in the cervical region is specifically discussed in thisdocument as an example, the present subject matter is applicable to anylead and/or electrode configuration and placement for vagal nervestimulation. Optimization of electrode placement and stimulationparameters using laryngeal activity is particularly useful when thetarget response of the neural stimulation is difficult to measureacutely and/or when the intended stimulation site is difficult to locateprecisely without a substantially invasive surgical procedure.

FIG. 1 is an illustration of an embodiment of a neural stimulationsystem 100 and portions of an environment in which system 100 is used.System 100 includes an activity sensor 110 for sensing laryngealactivity, a transvenous lead 112 for delivering vagal nerve stimulation,and an external system 120 coupled to activity sensor 110 via a cable111 and coupled to lead 112 via a cable 118. External system 120 allowsfor optimization of the vagal nerve stimulation using the sensedlaryngeal activity.

Lead 112 is a transvenous lead having a proximal end 114, a distal end113, and an elongate body 115 coupled between proximal end 114 anddistal end 113. Proximal end 114 includes a connector 117. In theillustrated embodiment, distal end 113 includes stimulation electrodes116A-B. As illustrated in FIG. 1, a body 101 includes a neck 102, aright internal jugular vein 104A, a left internal jugular vein 104B, aright subclavian vein 105A, and a left subclavian vein 105B. Lead 112 isinserted using techniques similar to those employed in implantingcardiac pacing leads. During the insertion, distal end 113 enters theleft subclavian vein 105B through an incision, advances in thesubclavian veins 105B and then 105A toward right internal jugular vein104A, enters right internal jugular vein 104A, advances in rightinternal jugular vein 104A until electrodes 116A-B reach one or morevagal nerve stimulation sites. After distal end 113 is in right internaljugular vein 104A, stimulation electrodes 116A-B are positioned, andrepositioned when necessary, using lead 112 and/or a lead insertion toolsuch as a stylet, a guide wire, or a guide catheter.

Electrodes 116A-B allow neural stimulation to be delivered to a vagusnerve 106, which is adjacent to right internal jugular vein 104A in thecervical region. Activity sensor 110 is placed on the neck over thelarynx to sense a signal indicative of laryngeal activity. The laryngealactivity is used as a measure of response of vagus nerve 106 to theneural stimulation delivered to vagus nerve 106. In various embodiments,the laryngeal activity is monitored for placement of stimulationelectrodes such as electrodes 116A-B, optimization of stimulationparameter such as those controlling stimulation intensity (e.g.,stimulation amplitude, frequency, duration, and duty cycle), anddetection or monitoring of various events that affect the response ofvagal nerve 106 to the neural stimulation.

As illustrated in FIG. 1, proximal end 114 remains outside of body 101,such as during an operation of implantation of lead 112 and animplantable medical device such as one discussed below with reference toFIG. 2. This allows electrodes 116A-B to be placed as desired beforeconnecting proximal end 114 to the implantable medical device. Proximalend 114 includes a connector 117 coupled to a connector 119 of cable 118to allow delivery of the neural stimulation from external system 120.External system 120 allows a user such as a physician or other caregiverto control the delivery of neural stimulation via lead 112 and monitorthe signal indicative of larynx sensed by activity sensor 110.

The configuration of system 100 shown in FIG. 1 is an example presentedfor illustrative purposes. The present subject matter generally includesmonitoring and optimization of vagal nerve stimulation delivered usingany electrode configuration using any signal that indicates laryngealactivity resulting from the vagal nerve stimulation. For example, lead112 may include one or more stimulation electrodes, and an electrodepair for delivering the neural stimulation may include two electrodes onlead 112 or an electrode on lead 112 and a reference electrode notnecessarily adjacent to the vagus nerve. In one embodiment, thereference electrode is a skin patch electrode for acute use. In oneembodiment, in addition to, or instead of, stimulation electrodes onlead 112 one or more nerve cuff electrodes each surrounding vagus nerve106 are used. In one embodiment, electrodes 116A-B are placed in theleft interval jugular vein 104B. During the insertion, distal end 113enters the left subclavian vein 105B or right subclavian vein 105Athrough an incision, enters left internal jugular vein 104B from rightsubclavian vein 105A, advances in left internal jugular vein 104B untilelectrodes 116A-B reach one or more vagal nerve stimulation sites.

FIG. 2 is an illustration of an embodiment of a neural stimulationsystem 200 and portions of the environment in which system 200 is used.System 200 differs from system 100 primarily in that the neuralstimulation is delivered from an implantable medical device 222implanted in body 101. In one embodiment, FIGS. 1 and 2 illustratedifferent stages of implantation and use of an implantable neuralstimulation system. FIG. 1 illustrates a system setup in the middle ofan implantation procedure during which lead 112 is inserted withelectrodes 116A-B placed to achieve desirable performance of vagal nervestimulation. FIG. 2 illustrates the system set-up after the implantableneural stimulation system is fully implanted, such as during the endstage of the implantation procedure when the implantable neuralstimulation system is programmed for chronic use or during a follow-upexamination during which the implantable neural stimulation system isadjusted if necessary.

An activity sensor 210 represents an embodiment of activity sensor 110that is capable of communicating with an external system 220 via awireless link. In one embodiment, activity sensor 110 and externalsystem 220 are electrically connected using a cable, and a communicationlink 211 represents the cable. In another embodiment, activity sensor110 and external system 220 are wirelessly coupled through telemetrysuch as a radio-frequency electromagnetic telemetry link, andcommunication link 211 represents the telemetry link.

Implantable medical device 222 delivers the neural stimulation throughone or both of electrodes 116A-B. After electrodes 116A-B are placed,proximal end 114 of lead 112 is connected to implantable medical device222 via connector 117. In one embodiment, the housing of implantablemedical device 222 functions as a reference electrode, and the neuralstimulation can be delivered using any pair of electrodes selected fromelectrodes 116A-B and the housing of implantable medical device 222. Inone embodiment, neural activity in vagus nerve 106 is sensed using anypair of electrodes selected from electrodes 116A-B and the housing ofimplantable medical device 222.

In one embodiment, in addition to the neural stimulation circuit,implantable medical device 222 includes other monitoring or therapeuticcircuits or devices such as one or more of cardiac pacemaker,cardioverter/defibrillator, drug delivery device, and biological therapydevice. External system 220 provides for control of and communicationwith implantable medical device 222 by the user. External system 220 andimplantable medical device 222 are communicatively coupled via atelemetry link 218. In one embodiment, external system 220 includes aprogrammer. In another embodiment, external system 220 is a patientmanagement system including an external device communicating withimplantable medical device 222 via telemetry link 218, a remote devicein a remote location, and a telecommunication network linking theexternal device and the remote device. The patient management systemallows access to implantable medical device 222 from the remotelocation, for purposes such as monitoring patient status and adjustingtherapies. In one embodiment, telemetry link 218 is an inductivetelemetry link. In an alternative embodiment, telemetry link 218 is afar-field radio-frequency telemetry link.

FIG. 3 is a block diagram illustrating an embodiment of portions of acircuit of system 100, including an activity sensor 310 coupled to anexternal system 320 by cable 111. Activity sensor 310 is an embodimentof activity sensor 110 and includes an accelerometer 331 to sense anacceleration signal being the signal indicative of laryngeal activity.Accelerometer 331 has characteristics suitable for sensing the magnitudeand frequency of vibrations of the larynx that indicate activity in thevagus nerve when vagal nerve stimulation is delivered. In oneembodiment, accelerometer 331 represents a plurality of accelerometersallowing for selection of an acceleration signal as the signalindicative of laryngeal activity based on the signal quality. Externalsystem 320 includes a neural stimulation analyzer 324, a neuralstimulation circuit 328, an external controller 329, and a userinterface 330. Neural stimulation analyzer 324 includes a laryngealactivity input 325, a neural stimulation input 326, and a processingcircuit 327. Laryngeal activity input 325 receives the signal indicativeof laryngeal activity from activity sensor 310 via cable 111. Neuralstimulation input 326 receives a signal indicative of the delivery ofthe neural stimulation to the vagus nerve. Processing circuit 327processes the signal indicative of laryngeal activity for analyzing theoperation and performance of system 100 using that signal. Neuralstimulation circuit 328 delivers the neural stimulation to stimulationelectrodes such as electrodes 116A-B. External controller 329 controlsoverall operation of external system 320, including the delivery of theneural stimulation from neural stimulation circuit 328. User interface330 allows the user to control the neural stimulation and monitor theresponse of the vagus nerve to the neural stimulation using the signalindicative of laryngeal activity.

FIG. 4 is a block diagram illustrating an embodiment of portion of acircuit of system 200, including an activity sensor 410 coupled to anexternal system 420 via communication link 211 and an implantablemedical device 422 coupled to external system 420 via telemetry link218. Activity sensor 410 is an embodiment of activity 210 and includesaccelerometer 331 and a sensor telemetry circuit 432. In the illustratedembodiment, communication link 211 is a telemetry link. Sensor telemetrycircuit 432 transmits the sensed signal indicative of laryngeal activityto external system 420 via telemetry link 211. In another embodiment,communication link 211 is a cable providing an electrical connectionbetween accelerometer 331 and laryngeal activity input 325. Externalsystem 420 includes neural stimulation analyzer 324, external telemetrycircuit 438, external controller 429, and user interface 330. Externaltelemetry circuit 438 receives the signal indicative of laryngealactivity from activity sensor 410 via communication link 211 andcommunicates with implantable medical device 422 via telemetry link 218to control the neural stimulation delivered from implantable medicaldevice 422. External controller 429 controls overall operation ofexternal system 420, including the transmission of commands forcontrolling the neural stimulation delivered from the implantablemedical device 422. Implantable medical device 422 includes a neuralstimulation circuit 434, an implant controller 435, and an implanttelemetry circuit 436. Neural stimulation circuit 434 delivers theneural stimulation through stimulation electrodes such as electrodes116A-B. Implant controller 435 controls the delivery of the neuralstimulation and is responsive to the commands transmitted from externalsystem 420. Implant telemetry circuit 436 receives the commands fromexternal system 420 via telemetry link 218 and when needed, transmitssignals to external system 420 via telemetry link 218.

FIG. 5 is an illustration of an embodiment of a laryngeal activitysensor assembly 540 that allows for a substantially stable attachment ofan activity sensor on a patient's neck over the larynx. Laryngealactivity sensor assembly 540 includes an activity sensor 510 and aneck-bracing structure configured to hold activity sensor 510 on theneck over the larynx. Activity sensor 510 senses the signal indicativeof laryngeal activity and represents any of activity sensors 110, 210,310, and 410. In the illustrated embodiment, a cable 511 is connected toactivity sensor 510 and has a connector 542 to provide electricalconnections between activity sensor 510 and external system 120 or 320.In a specific embodiment, cable 511 is detachably coupled to activitysensor 510. In another embodiment, activity sensor 510 iscommunicatively coupled to external system 220 or 420 via telemetry, andcable 511 is not needed.

Laryngeal activity sensor assembly 540 includes a neck brace 544 that isconfigured to wrap around a substantial portion of the neck and limitsthe movement of the neck. Neck brace 544 includes two ends 547A-B thatare separated by a substantial gap over an anterior portion of the neck.In one embodiment, neck brace 544 is made of a material selected tolimit the sensing of noise by activity sensor 510 by damping vibrationsof environmental sources such as vibrations from equipment and activityof medical personnel. In one embodiment, neck brace 544 is made of asubstantially soft material such as foam. Neck brace 544 has an interiorsurface 545 and an exterior surface 546. Interior surface 545 isconfigured for contacting the neck. In one embodiment, as illustrated inFIG. 5, neck brace 544 has a substantially even thickness betweeninterior surface 545 and exterior surface 546. This thickness is, forexample, between approximately 10 mm and 80 mm.

Laryngeal activity sensor assembly 540 further includes two brackets548-B each affixed onto one of ends 547A-B. Straps 549A-B are coupled tobrackets 548A-B and activity sensor 510. In one embodiment, straps549A-B represent different portions of a single strap. In anotherembodiment, straps 549A-B represent two straps each coupled betweenactivity sensor 510 and one of brackets 548A-B. Straps 549A-B areconfigured to press activity sensor 510 on the neck over the larynx fora substantially stable sensor placement. In one embodiment, straps549A-B are stretchable elastic straps. In one embodiment, at least oneof straps 549A-B is releasably coupled to one of brackets 547A-B. In oneembodiment, straps 549A-B are coupled to the brackets in a way allowingadjustment of a position of activity sensor 510 in cranial/caudaldirections.

In one embodiment, neck brace 544 is shaped to fit over the patient'shead and/or shoulders to further limit the relative movement betweenactivity sensor 510 and the larynx. In a specific embodiment, the edgeof neck brace 544 that is toward the caudal direction when worn by apatient includes a contour that approximately fits over the patient'sshoulders. This provides additional stability of sensor placement whenthe patient is sitting while the signal indicative of laryngeal activityis sensed.

FIG. 6 is an illustration of an embodiment of a laryngeal activitysensor assembly 640, which is an alternative embodiment to laryngealactivity sensor assembly 540. Laryngeal activity sensor assembly 640 issimilar to laryngeal activity sensor assembly 540 except for a neckbrace 644, which is made of a material similar or identical to that ofneck brace 544 but has a shape that is substantially different from thatof neck brace 544.

Neck brace 644 includes two ends 647A-B that are separated by asubstantial gap over an anterior portion of the neck. Brackets 548A-Bare each affixed to one of ends 647A-B. Neck brace 644 has an interiorsurface 645 and an exterior surface 646. Interior surface 644 isconfigured for contacting the neck. Exterior surface 646 is configuredto increase stability of the sensor placement by further limitingmovement of the neck. In one embodiment, as illustrated in FIG. 6,exterior surface 646 has a flat back portion 650 over the posteriorportion of the neck.

FIG. 7 is an illustration of an embodiment of an activity sensor 710.Activity sensor 710 is an embodiment of activity sensor 510 thatincludes an accelerometer 731 affixed onto a sensor base 754.Accelerometer sensor 731 represents a specific embodiment ofaccelerometer 331 and senses the signal indicative of laryngealactivity. Sensor base 754 is configured to be an interface betweenaccelerometer sensor 731 and the neck, and has a surface 755 curved tofit onto the neck.

FIG. 8 is an illustration of an embodiment of an activity sensor 810.Activity sensor 810 is an embodiment of activity sensor 710 and includesaccelerometer 731 and a sensor base 854. Sensor base 854 has a surface855 curved to fit onto the neck of a male patient over part of histhyroid cartilage. In one embodiment, as illustrated in FIG. 8, surface855 includes a recess 856 on one end and a notch 857 at the other endfor fitting over part of the thyroid cartilage.

FIG. 9 is a block diagram illustrating an embodiment of a processingcircuit 927, which is a specific embodiment of processing circuit 327.Processing circuit 927 includes a signal conditioning circuit 960, astimulation threshold analyzer 962, a lead status analyzer 966, a neuralinjury analyzer 968, and a presentation processing circuit 970.

Signal conditioning circuit 960 conditions the signal indicative oflaryngeal activity for analysis or presentation purposes. Signalconditioning circuit 960 increases the signal-to-noise ratio of thesignal indicative of laryngeal activity, where the signal includescomponents of the signal indicative of laryngeal activity that resultfrom the vagal nerve stimulation, and the noise includes components ofthe signal indicative of laryngeal activity that is not an effect of thevagal nerve stimulation. Signal conditioning circuit 960 includes afilter 961 that filters out the noise. In one embodiment, filter 961 hasa pass-band selected based on the frequency at which neural stimulationpulses are delivered to the vagus nerve.

Stimulation threshold analyzer 962 automatically measures a stimulationthreshold associated with each pair of stimulation electrodes via whichthe neural stimulation is delivered to the vagus nerve, such asstimulation electrodes 116A-B. The stimulation threshold is the minimumstimulation intensity at which the neural stimulation activates thevagus nerve. Stimulation threshold analyzer 962 includes a comparator963 and a stimulation intensity controller 964. Comparator 963 includesa first input 963A to receive an amplitude of the signal indicative oflaryngeal activity, a second input 963B to receive a nerve capturethreshold, and an output 963C that indicates a nerve capture when theamplitude of the signal indicative of laryngeal activity exceeds thenerve capture threshold. That is, an amplitude of the signal indicativeof laryngeal activity that exceeds the nerve capture threshold is theindication that the neural stimulation has elicited action potentialspropagating in the vagus nerve. In various embodiments, the nervecapture threshold is determined empirically based a patient populationor each individual patient. Stimulation intensity controller 964 adjuststhe stimulation intensity of the neural stimulation such that aplurality of stimulation intensities may be tested, and stimulationthreshold analyzer 962 automatically determines the stimulationthreshold by selecting the tested minimum stimulation intensity thatresults in a nerve capture. In various embodiments in which the neuralstimulation includes delivery of electrical pulses, the stimulationintensity is controlled by stimulation amplitude (voltage or current)and/or stimulation pulse width. Stimulation intensity controller 964adjusts the stimulation intensity by adjusting the stimulationamplitude, the stimulation pulse width, or both. In one embodiment,stimulation intensity controller 964 increases the stimulation intensityfrom an initial intensity until the nerve capture is indicated or aspecified maximum stimulation intensity is reached. If the maximumstimulation intensity is reached before the nerve capture is indicated,the stimulation electrodes are repositioned before the determination ofthe stimulation threshold continues. In one embodiment, stimulationthreshold analyzer 962 presents the minimum capture intensity at whichthe nerve capture is indicated when the stimulation intensity is beingincreased as the stimulation threshold. In another embodiment, after theminimum capture intensity is reached, stimulation intensity controller964 decreases the stimulation intensity from that minimum captureintensity until the nerve capture is no longer indicated. Stimulationthreshold analyzer 962 presents the minimum stimulation intensity atwhich the nerve capture is indicated when the stimulation intensity isbeing decreased as the stimulation threshold.

Lead status analyzer 966 detects dislodgment or breakage of a lead fordelivering the neural stimulation, such as lead 112, by detecting asubstantial change in the stimulation threshold between two stimulationthreshold measurements. In one embodiment, upon detection of thedislodgment or breakage of the lead, lead status analyzer 966 produces awarning signal or message to be presented to the user through userinterface 330.

Neural injury analyzer 968 detects a nerve injury by monitoring thechange in the stimulation threshold and/or the change in the amplitudeof the signal indicative of laryngeal activity over time. The laryngealnerves include efferent nerve fibers. A neural injury occurring in thenervous path between the stimulation site and the larynx is indicated byabsence or weakening of laryngeal response to the vagal nervestimulation. A weakened laryngeal response may serve as an earlyindication of the neural injury. Appropriate treatments may be appliedin response, thereby preventing the neural injury from progressing to adegree associated with a major functional impairment. In one embodiment,neural injury analyzer 968 monitors the change in the stimulationthreshold over time, determines the speed of the change in thestimulation threshold, and detects a neural injury based on the speed ofthe change in the stimulation threshold. In another embodiment, neuralinjury analyzer 968 monitors the amplitude of the signal indicative oflaryngeal activity in response to delivering the neural stimulation at aspecified stimulation intensity over time, determines the speed of thechange in the amplitude of the signal indicative of laryngeal activity,and detects a neural injury based on the speed of the change in theamplitude of the signal indicative of laryngeal activity. In anotherembodiment, neural injury analyzer 968 detects a substantial change inneural conduction velocity as an indication of neural injury. In aspecific embodiment, neural injury analyzer 968 measures the neuralconduction velocity as the ratio of a neural conduction time to anestimated neural conduction distance, and detects a neural injury basedon the change in the neural conduction velocity over time. The neuralconduction time is the time interval between the delivery of a stimulusand the beginning of the elicited response in the signal indicative oflaryngeal activity. In another specific embodiment, neural injuryanalyzer 968 measures the neural conduction time being the time intervalbetween the delivery of a stimulus and the beginning of the elicitedresponse in the signal indicative of laryngeal activity, and detects aneural injury based on the change in the neural conduction time overtime. In one embodiment, upon detection of a possible neural injury,neural injury analyzer 968 produces a warning signal or message to bepresented to the user through user interface 330.

Presentation processing circuit 970 processes the signal indicative oflaryngeal activity for presentation to the user in one or more formsthrough user interface 330. In one embodiment, presentation processingcircuit 970 also processes other signals, messages, and/or indicatorsrelated to laryngeal activity, lead status, neural injury, and/or otherrelated information for presentation to the user through user interface330.

FIG. 10 is a block diagram illustrating an embodiment of a userinterface 1030. User interface 1030 is a specific embodiment of userinterface 330 and includes a presentation device 1072 and a user inputdevice 1080. Presentation device 1072 presents indicators of thelaryngeal activity and the neural stimulation in one or more forms. Userinput device 1080 allows the user to control the neural stimulation byentering commands and parameters, and to control presentation device1080 by choosing how the laryngeal activity and the neural stimulationare indicated.

In the illustrated embodiment, presentation device 1072 includes anaudio presentation device 1074 and a visual presentation device 1076.Audio presentation device 1074 includes a speaker 1075 that generates anaudible tone indicative of the laryngeal activity. The audible tone hasa pitch indicative a frequency at which the larynx vibrates and/or amagnitude of the laryngeal activity. In one embodiment, the audible tonehas a pitch indicative the frequency at which the larynx vibrates and avolume indicative of the magnitude of the laryngeal activity. When theneural stimulation is delivered as electrical pulses, as the stimulationfrequency (the frequency at which the electrical pulses are delivered)increases, the muscular response in the larynx may change from a twitchresponse to a tentatic response (which means the muscle stays contractedduring the delivery of an entire pulse train). In one embodiment, thestimulation frequency is selected such that the delivery of theelectrical pulses elicits a twitch response but not a tentatic response.Thus, the frequency at which the larynx vibrates is the stimulationfrequency, and the magnitude of the laryngeal activity is a function ofthe stimulation intensity.

Visual presentation device 1076 includes a screen 1077, light-emittingdiodes (LEDs) 1078, and a gauge 1079. Screen 1077 displays the signalindicative of laryngeal activity and a signal indicative of the neuralstimulation. Examples of the signal indicative of the neural stimulationinclude neural stimulation markers and a neural signal indicative ofvagal nerve activity sensed by the stimulation electrodes such aselectrodes 116A-B. In various embodiments, screen 1077 further displaysone or more sensed physiological signals such as electrocardiogram (ECG)and various signals, messages, and/or indicators related to laryngealactivity, lead status, neural injury, and/or other related information.LEDs 1078 are each turned on when the amplitude of the signal indicativeof laryngeal activity exceeds a predetermined threshold. A plurality ofdifferent thresholds each associated with one or more of LEDs 1078allows for selective lighting of each of LEDs 1078 according to theamplitude of the signal indicative of laryngeal activity. Gauge 1079indicates the magnitude of the laryngeal activity. In one embodiment,gauge 1079 is in the form of an image displayed in screen 1077. Inanother embodiment, gauge 1079 is a device separated from screen 1077.

FIG. 11 is an illustration of an external programmer 1120, which is anembodiment of external system 120, 220, 320, or 420. In the illustratedembodiment, external programmer 1120 includes speaker 1075, screen 1077,LEDs 1078, and gauge 1079. In other embodiments, external programmer1120 includes any one or more of speaker 1075, screen 1077, LEDs 1078,and gauge 1079. In the illustrated embodiment, screen 1077 includes atrace of the signal indicative of laryngeal activity, a signalindicative of the neural stimulation, a trace and an ECG signal, and anarea 1182 displaying the various signals, messages, and/or indicatorsrelated to laryngeal activity, lead status, neural injury, and/or otherrelated information.

Programmer 1120 receives the signal indicative of laryngeal activity andcontrols the neural stimulation by allowing the user to enter commandsand parameters. In the illustrated embodiment, programmer 1120 includesa sensor input 1184 and a stimulation output 1185. Activity sensor 510senses the signal indicative of laryngeal activity and transmits thesensed signal to programmer 1120 through cable 511 and connector 542,which is detachably connected to sensor input 1184. Cable 118 with aconnector 1187 detachably connected to stimulation output 1185 andconnector 119 provides for connection to stimulation electrodes such asstimulation electrodes 116A-B on lead 112. This allows for delivery ofthe neural stimulation from a neural stimulation circuit of programmer1120. In one embodiment, programmer 1120 is also capable of receivingthe signal indicative of laryngeal activity from activity sensor 510 viatelemetry. In one embodiment, programmer 1120 is also capable ofcontrolling the delivery of the neural stimulation from a neuralstimulation circuit of an implantable medical device via telemetry.

FIG. 12 is a flow chart illustrating an embodiment of a method 1200 foranalyzing effect of neural stimulation using a signal indicative oflaryngeal activity. In one embodiment, method 1200 is performed bysystems 100 or 200.

The signal indicative of laryngeal activity is sensed at 1210. Theneural stimulation is delivered to the vagus nerve at 1220. The signalindicative of laryngeal activity is conditioned at 1230, to isolatelaryngeal activity resulting from the delivery of the neural stimulationfrom other components of the sensed signal indicative of laryngealactivity. An effect of the delivery of the neural stimulation isanalyzed at 1240 using the signal indicative of laryngeal activity.Indicators of the laryngeal activity and the delivery of the neuralstimulation are presented at 1250. In one embodiment, an audible toneindicative of the laryngeal activity is generated. In a specificembodiment, the audible tone has a pitch indicative a magnitude of thelaryngeal activity. In another specific embodiment, the audible tone hasa pitch indicative a frequency at which the larynx vibrates and a volumeindicative of a magnitude of the laryngeal activity. In anotherembodiment, a visual indication of the laryngeal activity is produced.Examples of the visual indication include traces of the signalindicative of laryngeal activity, a signal indicative of the neuralstimulation, and a gauge indicative of magnitude of the laryngealactivity.

FIG. 13 is a flow chart illustrating an embodiment of a method 1300 forautomatically determining a stimulation threshold for the neuralstimulation using the signal indicative of laryngeal activity. Thestimulation threshold is indicative of the minimum stimulation intensityrequired to capture the vagus nerve. In one embodiment, method 1300 isperformed by stimulation threshold analyzer 962.

The stimulation intensity (SI) of the neural stimulation is set to aninitial intensity at 1310. In one embodiment, the initial intensity isan empirically determined parameter. In one embodiment, the initialintensity is selected by the user. When the neural stimulation isdelivered as electrical pulses, the SI is controlled by the (voltage orcurrent) and the pulse width of each of the electrical pulses.

The neural stimulation is delivered to the vagus nerve at the SI at1312. A nerve capture is being detected using the signal indicative oflaryngeal activity at 1314, by comparing the amplitude of the signalindicative of laryngeal activity to a nerve capture threshold. The nervecapture is detected at 1316 if the amplitude of the signal indicative oflaryngeal activity exceeds the nerve capture threshold.

If the nerve capture is not detected at 1316, whether the SI has reacheda specified maximum SI is determined at 1318. If the SI has reached thespecified maximum SI at 1320, the stimulation electrodes arerepositioned, or other approaches must be taken to increase thespecified maximum SI and/or decrease the stimulation threshold, at 1324.In one embodiment, the stimulation electrodes are “repositioned”, orselected, electronically. The neural stimulation is delivered to thevagus nerve using an active set of stimulation electrodes electronicallyselected from multiple available sets of stimulation electrodes, andelectronically repositioning means electronically selecting a differentset of available stimulation electrodes to be the active set ofstimulation electrodes. If the SI has not reached the specified maximumSI at 1320, the SI is increased by ΔSI at 1322, and method 1300 returnsto 1312 to continue therefrom. In one embodiment, the stimulationthreshold is determined as a voltage of an electrical pulse at aspecified pulse width. In a specific embodiment, ΔSI is about 0.2 V.

If the nerve capture is detected at 1316, the current SI is the minimumcapture intensity at which the nerve capture is detected as thestimulation intensity is being increased. The SI is decreased from thatminimum capture intensity, with ΔSI′ being the decrement step, at 1326.In one embodiment, ΔSI′ and ΔSI are set to the same value. In a specificembodiment, ΔSI′ is about 0.2 V.

The neural stimulation is delivered at the (decreased) SI at 1328. Anerve capture is being detected using the signal indicative of laryngealactivity at 1330, by comparing the amplitude of the signal indicative oflaryngeal activity to the nerve capture threshold. The nerve capture isdetected at 1332 if the amplitude of the signal indicative of laryngealactivity exceeds the nerve capture threshold.

If the nerve capture is detected at 1332, method 1300 returns to 1326 tofurther decrease the SI and continue therefrom. If the nerve capture isnot detected at 1332, the SI prior to the last decrease at 1326 is setto the stimulation threshold at 1334. That is, the stimulation threshold(ST) is the current SI (after 1326) plus ΔSI′.

FIG. 14 is a flow chart illustrating an embodiment of a method 1400 formonitoring and titrating the neural stimulation acutely and chronicallyusing the signal indicative of laryngeal activity. Method 1400 isperformed during and after the implantation of an implantable neuralstimulation system. In one embodiment, method 1400 is performed withsystems 100 and/or 200.

The signal indicative of laryngeal activity is sensed at 1410. Theneural stimulation is delivered to the vagus nerve at 1420. Thelaryngeal activity indicates the response of the vagus nerve to theneural stimulation. The response depends on, for example, the positionof the stimulation electrodes, stimulation parameters, condition of theneural stimulation system such as condition of the leads and/orstimulation electrodes, existence and progress of neural injury, andhealing of tissue surrounding the stimulation electrodes followingimplantation of the stimulation electrodes.

The delivery of the neural stimulation is optimized during theimplantation of an implantable medical device at 1430. This includes,for example, positioning a stimulation electrode at 1432 and optimizingstimulation parameters associated with that stimulation electrode at1434. In various embodiments, 1432 and 1434 are performed for eachstimulation electrode or each pair of stimulation electrodes. Thestimulation electrode is placed for delivering the neural stimulation tothe vagus nerve using the signal indicative of laryngeal activity. Inone embodiment, the stimulation electrode is incorporated onto thedistal end of a transvenous lead. The transvenous lead is inserted intothe vascular system such that the stimulation electrode is in a positionwithin an approximate target region in an internal jugular vein. Astimulation threshold is determined automatically, such as by performingmethod 1300, for that position using the signal indicative of laryngealactivity. If the stimulation threshold is not satisfactory, thestimulation electrode is placed in another position within theapproximate target region, and the stimulation threshold is determinedfor the new position. The repositioning and threshold determination arerepeated until a satisfactory stimulation threshold is obtained. In oneembodiment, the repositioning is performed electronically. The neuralstimulation is delivered using an active stimulation electrodeelectronically selected from a plurality of available stimulationelectrodes, and placing a stimulation electrode in another positionmeans electronically selecting an available stimulation electrode placedin another position to be the active stimulation electrode. In anotherembodiment, after the transvenous lead is inserted and the stimulationelectrode is in the position within the approximate target region, aminimal electrical current is delivered to the vagus nerve using thestimulation electrode. The amplitude is kept low but sufficient toproduce laryngeal activity that can be sensed. The amplitude of thesignal indicative of laryngeal activity is monitored while thestimulation electrode is moved to evaluate positions within theapproximate target region. The stimulation electrode is positionedpermanently in the location associated with a maximum amplitude of thesignal indicative of laryngeal activity.

After the stimulation electrode is positioned at 1432, the stimulationparameters associated with the stimulation electrode are optimized at1434. In one embodiment, this includes determining the stimulationthreshold associated with the stimulation electrode automatically, suchas by performing method 1300, for the permanent position of thestimulation electrode. The stimulation intensity associated with thestimulation electrode is programmed for chronic use based on thestimulation threshold, such as by setting the stimulation intensity to avalue exceeding the stimulation threshold by a predetermined margin.

The delivery of the neural stimulation is monitored and titrated afterthe device implantation at 1440. This includes, for example, optimizingstimulation parameters at 1442, monitoring a lead or stimulationelectrode status at 1444, detecting a neural injury at 1446, andmonitoring a healing process at 1448. In various embodiments, 1440, orany portion thereof, is performed by the user during a follow-upexamination according a specified schedule, such as on an approximatelyperiodic basis.

The stimulation parameters are optimized at 1442. In one embodiment,this includes determining the stimulation threshold associated with eachstimulation electrode automatically, such as by performing method 1300.If the stimulation threshold associated with an electrode has changedsubstantially from the previous measurement, the stimulation intensityassociated with that stimulation electrode is adjusted based on the newstimulation threshold, such as by setting the stimulation intensity to avalue exceeding the new stimulation threshold by a predetermined margin.

The lead or stimulation electrode status is monitored at 1444. Thisincludes, for example, detection of possible displacement, dislodgement,and breakage of the lead. A possible lead problem is indicated by asubstantial, abnormal change in the stimulation threshold betweenmeasurements of the stimulation threshold.

A neural injury is detected at 1446. In one embodiment, the neuralinjury is detected by monitoring the change in the stimulation thresholdover time. A possible neural injury is indicated by a detected abnormalspeed of change in the stimulation threshold. In another embodiment, theneural injury is detected by monitoring the amplitude of the signalindicative of laryngeal activity in response to delivering neuralstimulation at a specified stimulation intensity over time. A possibleneural injury is indicated by a detected abnormal speed of the change inthe amplitude of the signal indicative of laryngeal activity. The neuralinjury detection at 1446 allows for early discovery of a neural injurythat needs immediate treatment to prevent from developing into a majorfunctional impairment.

A healing process is monitored at 1448. After the implantation of theimplantable medical device and the lead or stimulation electrodes, itmay take weeks or months for the tissue injured during the implantationto heal and the interface between the body and the implanted system tostabilize. This healing process is monitored by monitoring the change inthe stimulation threshold over time. A stabilized stimulation thresholdis an indication that the healing process may have substantiallycompleted.

It is to be understood that the above detailed description is intendedto be illustrative, and not restrictive. Other embodiments will beapparent to those of skill in the art upon reading and understanding theabove description. The scope of the invention should, therefore, bedetermined with reference to the appended claims, along with the fullscope of equivalents to which such claims are entitled.

1. A neural stimulation system for applying neural stimulation to a body having a neck, a larynx, and a vagus nerve, the system comprising: an activity sensor adapted to sense a signal indicative of laryngeal activity; a laryngeal activity sensor assembly including a neck-bracing structure configured to hold the activity sensor on the neck over the larynx; and a neural stimulation analyzer communicatively coupled to the activity sensor, the neural stimulation analyzer including: a laryngeal activity input to receive the signal indicative of laryngeal activity; a neural stimulation input to receive a signal indicative of a delivery of the neural stimulation to the vagus nerve; and a processing circuit coupled to the laryngeal activity input and the neural stimulation input, the processing circuit configured to process the signal indicative of laryngeal activity for analyzing the neural stimulation system using the signal indicative of laryngeal activity.
 2. The neural stimulation system of claim 1, wherein the activity sensor comprises an accelerometer adapted to sense an acceleration signal being the signal indicative of laryngeal activity.
 3. A neural stimulation system for applying neural stimulation to a body having a neck, a larynx, and a vagus nerve, the system comprising: an activity sensor adapted to sense a signal indicative of laryngeal activity; a laryngeal activity sensor assembly including the activity sensor and a neck brace configured to wrap around a portion of the neck; and a neural stimulation analyzer communicatively coupled to the activity sensor, the neural stimulation analyzer including: a laryngeal activity input to receive the signal indicative of laryngeal activity; a neural stimulation input to receive a signal indicative of a delivery of the neural stimulation to the vagus nerve; and a processing circuit coupled to the laryngeal activity input and the neural stimulation input, the processing circuit configured to process the signal indicative of laryngeal activity for analyzing the neural stimulation system using the signal indicative of laryngeal activity.
 4. The neural stimulation system of claim 3, wherein the neck brace comprises two ends separated by a gap over an anterior portion of the neck, and the laryngeal activity sensor assembly further comprises: brackets each affixed onto one of the two ends of the neck brace; and one or more straps coupled to the brackets and the activity sensor, the one or more straps configured to press the activity sensor on the neck over the larynx.
 5. The neural stimulation system of claim 4, wherein the one or more straps are coupled to the brackets in a way allowing adjustment of a position of the activity sensor in cranial/caudal directions.
 6. The neural stimulation system of claim 4, wherein the activity sensor comprises a sensor base including a surface curved to fit onto the neck.
 7. A neural stimulation system for applying neural stimulation to a body having a neck, a larynx, and a vagus nerve, the system comprising: an activity sensor adapted to sense a signal indicative of laryngeal activity; and a neural stimulation analyzer communicatively coupled to the activity sensor, the neural stimulation analyzer including: a laryngeal activity input to receive the signal indicative of laryngeal activity; a neural stimulation input to receive a signal indicative of a delivery of the neural stimulation to the vagus nerve; a signal conditioning circuit adapted to increase a signal-to-noise ratio of the signal indicative of laryngeal activity, the signal including components of the signal indicative of laryngeal activity resulting from the neural stimulation; and a processing circuit coupled to the laryngeal activity input and the neural stimulation input, the processing circuit configured to process the signal indicative of laryngeal activity for analyzing the neural stimulation system using the signal indicative of laryngeal activity.
 8. The neural stimulation system of claim 7, comprising a laryngeal activity sensor assembly including a neck-bracing structure configured to hold the activity sensor on the neck over the larynx.
 9. The neural stimulation system of claim 7, further comprising: stimulation electrodes to deliver the neural stimulation to the vagus nerve; and a neural stimulation circuit, coupled to the stimulation electrodes, to deliver neural stimulation pulses through to the vagus nerve through the stimulation electrodes.
 10. The neural stimulation system of claim 9, further comprising a presentation device adapted to present indicators of the laryngeal activity and the delivery of the neural stimulation pulses.
 11. The neural stimulation system of claim 9, wherein the neural stimulation analyzer comprises a stimulation threshold analyzer adapted to measure at least one stimulation threshold automatically, the stimulation threshold being a minimum stimulation intensity required for the neural stimulation pulses to elicit a neural response in the vagus nerve.
 12. The neural stimulation system of claim 11, wherein the stimulation threshold analyzer comprises a comparator including a first input to receive an amplitude of the signal indicative of laryngeal activity, a second input to receive a nerve capture threshold, and an output indicative of a nerve capture when the amplitude of the signal indicative of laryngeal activity exceeds the nerve capture threshold.
 13. The neural stimulation system of claim 12, wherein the stimulation threshold analyzer comprises a stimulation intensity controller adapted to increase a stimulation intensity from an initial intensity until the nerve capture is indicated or a predetermined maximum stimulation intensity is reached.
 14. The neural stimulation system of claim 13, wherein the stimulation intensity controller is further adapted to decrease the stimulation intensity, after the nerve capture is indicated, until the nerve capture is no longer indicated.
 15. The neural stimulation system of claim 11, further comprising a transvenous lead including: a proximal end coupled to the neural stimulation circuit; a distal end including at least one of the stimulation electrodes; and an elongate body coupled between the proximal end and the distal end.
 16. The neural stimulation system of claim 15, wherein the neural stimulation analyzer comprises a lead status analyzer adapted to produce a warning of lead dislodgment or breakage based on the change in the at least one stimulation threshold associated with the at least one of the stimulation electrodes included in the distal end of the lead between measurements of that stimulation threshold.
 17. The neural stimulation system of claim 11, wherein the neural stimulation analyzer comprises a neural injury analyzer adapted to detect a nerve injury by monitoring one or more of a change in the at least one stimulation threshold over time, a change in the amplitude of the signal indicative of laryngeal activity over time, and a change in a neural conduction velocity over time.
 18. The neural stimulation system of claim 9, further comprising: an implantable medical device including the neural stimulation circuit; and an external system communicatively coupled to the implantable medical device via telemetry, the external system including the neural stimulation analyzer.
 19. A neural stimulation system for applying neural stimulation to a body having a neck, a larynx, and a vagus nerve, the system comprising: an activity sensor adapted to sense a signal indicative of laryngeal activity; a laryngeal activity sensor assembly configured to hold the activity sensor on the neck over the larynx; a signal conditioning circuit, communicatively coupled to the activity sensor, to condition the signal indicative of laryngeal activity; a neural stimulation circuit adapted to deliver the neural stimulation to the vagus nerve; and a presentation device coupled to the signal conditioning circuit and the neural stimulation circuit, the presentation device adapted to present indicators of the laryngeal activity and the delivery of the neural stimulation.
 20. The neural stimulation system of claim 19, wherein the activity sensor comprises an accelerometer.
 21. The neural stimulation system of claim 19, wherein the presentation device comprises a speaker configured to produce an audible tone indicative of the laryngeal activity.
 22. The neural stimulation system of claim 19, wherein the presentation device comprises a visual indicator configured to produce a visual indication of the laryngeal activity.
 23. The neural stimulation system of claim 22, wherein the visual indicator comprises a screen displaying the signal indicative of laryngeal activity and a signal indicative of the neural stimulation.
 24. The neural stimulation system of claim 22, wherein the visual indicator comprises one or more light-emitting diodes each turned on when an amplitude of the signal indicative of laryngeal activity exceeds a threshold.
 25. The neural stimulation system of claim 22, wherein the visual indicator comprises a gauge indicative of a magnitude of the laryngeal activity.
 26. A method for applying neural stimulation to a body having a neck, a larynx, and a vagus nerve, the method comprising: sensing a signal indicative of laryngeal activity; delivering the neural stimulation to the vagus nerve; conditioning the signal indicative of laryngeal activity to isolate laryngeal activity resulting from the delivery of the neural stimulation; and presenting indicators of the laryngeal activity.
 27. The method of claim 26, wherein presenting the indicators of the laryngeal activity comprises producing an audible tone indicative of the laryngeal activity, the audible tone having a pitch indicative at least one of a frequency at which the larynx vibrates and a magnitude of the laryngeal activity.
 28. The method of claim 27, wherein presenting the indicators of the laryngeal activity comprises displaying the signal indicative of laryngeal activity on a screen.
 29. The method of claim 27, wherein presenting the indicators of the laryngeal activity comprises presenting a magnitude of the laryngeal activity using light emitting diodes.
 30. The method of claim 27, wherein presenting the indicators of the laryngeal activity comprises presenting a magnitude of the laryngeal activity using a gauge.
 31. The method of claim 26, further comprising determining a stimulation threshold automatically using the signal indicative of laryngeal activity, the stimulation threshold indicative of a minimum stimulation intensity required to capture the vagus nerve by the neural stimulation.
 32. The method of claim 31, wherein determining the stimulation threshold automatically comprises: setting a stimulation intensity of the neural stimulation to an initial intensity; detecting a nerve capture by comparing the amplitude of the signal indicative of laryngeal activity to a nerve capture threshold; and increasing the stimulation intensity from the initial intensity until the nerve capture is detected or if a predetermined maximum stimulation intensity is reached before the nerve capture is detected.
 33. The method of claim 32, wherein determining the stimulation threshold automatically further comprises decreasing the stimulation intensity, after the nerve capture is detected, until the nerve capture is no longer detected, and further comprising presenting a minimum intensity at which the nerve capture is detected when the stimulation intensity is being decreased as the stimulation threshold.
 34. The method of claim 31, further comprising detecting a lead dislodgement or breakage by monitoring a change in the stimulation threshold over two or more measurements of the stimulation threshold.
 35. The method of claim 31, further comprising detecting a neural injury by monitoring a change in the stimulation threshold over time.
 36. The method of claim 35, further comprising detecting a neural injury by monitoring a change in a neural conduction velocity over time.
 37. The method of claim 26, wherein delivering the neural stimulation to the vagus nerve comprises delivering neural stimulation pulses through a stimulation electrode, and further comprising positioning the stimulation electrode by using the laryngeal activity for guidance.
 38. The method of claim 37, further comprising monitoring a tissue healing process following an implantation of the stimulation electrode by monitoring a change in the stimulation threshold over time.
 39. The method of claim 37, wherein positioning the stimulation electrode comprises electronically selecting one or more active stimulation electrodes from a plurality of available stimulation electrodes. 